The present invention relates to a mechanism for clamping a cutting insert used in a rotary cutting tool such as a face milling cutter. It also relates to a cutting insert to be clamped by the mechanism.
Researchers and engineers have been improving the cutting method for soft materials such as aluminum alloys in order to increase machining precision and productivity. In particular, in the field of the milling of soft aluminum alloys, the cutting efficiency has increased notably by employing high-speed rotation in comparison with the cutting of ordinary steel materials. In other words, cutting tools have been rotated at increasingly high speeds. Cutting tools for milling aluminum alloys usually use cemented-carbide inserts and coated inserts. However, the use of polycrystalline-diamond (PCD) inserts has been increasing in recent years. PCD inserts can prevent the aluminum component from welding onto the cutting edge, improving the finishing precision. Consequently, PCD inserts can have sufficient resistance to high-speed cutting.
When a cutting tool is operated at high rotational speeds to increase efficiency, considerable centrifugal force is applied to the peripheral portion of the cutting tool. The force may scatter cutting inserts and insert-holding parts to the outside, and become a serious safety hazard. Therefore, it is necessary to solve this potential problem prior to the application of high-speed operation. A number of proposals to prevent scattering have been disclosed thus far.
FIG. 7 is an example of the prior art for securing a cutting insert (hereinafter referred to as insert) with a wedging member. This example has been disclosed by the published Japanese patent application Tokukaihei 5-138426. In FIG. 7, the individual members are denoted by the following numbers: 1: a tool body; 2: an insert; 3: a wedging member; 4: a clamping bolt; 5: a holding member; 6: a recess; and 7: a projection. The insert 2 is held by fitting the projection 7 provided on the front face of the holding member 5 into the recess 6 provided on the rear face of the insert 2. This patent application has also disclosed another structure in which the insert 2 is directly held by fitting the projection 7 provided directly on the tool body into the recess 6 without using the holding member 5.
The wedging member 3 is held such that the turning of the clamping bolt 4 can move the wedging member 3 back and forth in the radial direction of the tool body 1. Thus, one side of the wedging member 3 presses the front face of the insert 2 to prevent it from springing out. When loosened, the wedging member 3 and the clamping bolt 4 can move in the axial direction of the tool body 1, facilitating the attaching and detaching of the insert 2.
Another published Japanese patent application, Tokukai 2000-15503, has disclosed another method for preventing the spring-out of an insert by using a wedging member. In this application, the fitting of the insert is performed by replacing the recess of the insert shown in FIG. 7 with a through hole and concurrently replacing the projection of the holding member with a pinning member. Yet another published Japanese patent application, Tokukaihei 11-10435, has disclosed another method. This method not only prevents the spring-out of an insert by pressing the slanted face of the insert or a holding member with a wedging member but also enables the draw-out of the insert or the holding member in the axial direction of the tool body. This structure allows easy attachment and detachment of the insert or the holding member merely by slightly loosening the wedging member.
In the above description, when an insert is attached by the fitting of the recess and the projection or by the fitting of the through hole and the pin, a clearance must be provided at the fitting portion for enabling easy attachment and detachment of the insert. This clearance, however, allows the insert to shift by the amount of the clearance when centrifugal force is applied during high-speed rotation. This shift disturbs, the balanced amounts of the cutting among the inserts, causing uneven thicknesses of the metal chips produced by the cutting operation. As a result, an excessive load is applied to the shifted insert. This load may cause a fracture and subsequent spring-out of the insert.
Although the fixing of the insert with the wedging member can prevent the shift and spring-out of the insert, the centrifugal force may cause the wedging member itself to spring out because the wedging member is attached without restriction in the direction of the centrifugal force. Furthermore, the use of the wedging member is unavoidably accompanied by the reduction in the stiffness of the tool body. The intense tightening force broadens the groove that houses the insert and wedging member, generating distortion and strain in the tool body. When centrifugal force is applied due to high-speed rotation of the tool, the distortion and strain will be released, increasing the risk of the spring-out of the wedging member.
Yet another published Japanese patent application, Tokuhyouhei 10-508259, has disclosed another method shown in FIG. 8. This method attaches an insert without using a recess-projection fit or a pin fit and yet without using a wedging member. In FIG. 8, the individual members are denoted by the following numbers: 11: a tool body; 12: an insert; 13: a cartridge (holding member); 14: an insert-attaching screw; 15: a cartridge-receiving recess; 16: a holding screw; 17: an adjusting screw; 18: a threaded hole; and 19: a set screw.
As shown in FIG. 8, the insert 12 is attached to the tool body 11 through the cartridge 13. The insert 12 is positioned in a pocket 13a of the cartridge without being turned and is fixed by the insert-attaching screw 14. The cartridge 13 is fixed in the cartridge-receiving recess 15 of the tool body 11 with the holding screw 16 and the set screw 19.
A cartridge hole 13b into which the holding screw 16 is inserted has a diameter slightly larger than that of the holding screw 16 so that the position of the cartridge 13 can be adjusted upward and downward and leftward and rightward. The upward and downward adjustment of the cartridge 13 is performed by inserting the adjusting screw 17 into an inclined hole 13c provided at an upper portion of the cartridge 13. This adjustment controls the amount of the front protrusion of the insert 12.
The cartridge-receiving recess 15 has an inner wall 15a that is parallel to its position""s tangent on the peripheral circle of the tool body 11 and a side wall 15b that is slanted to the normal direction of the inner wall 15a by an angle of about 10 degrees. The cartridge 13 to be mated with these walls has a back face 13d and a side face 13e between which the same angle as above is provided. The threaded hole 18 is provided from the peripheral surface of the tool body 11 to the cartridge-receiving recess 15. The set screw 19 is screwed into the threaded hole 18 to press the other side face 13f of the cartridge 13, so that the back face 13d and the side face 13e of the cartridge 13 are strongly mated with the inner wall 15a and the side wall 15b of the recess 15, respectively. Thus, the cartridge 13 is fixed.
The side face 13f of the cartridge 13 has an indentation (not shown in FIG. 8) into which the end of the set screw 19 is fitted. The spring-out of the cartridge 13 due to the centrifugal force is prevented by fitting the set screw 19 into the indentation and by pressing the side face 13e of the cartridge against the side wall 15b having an acute angle to the inner wall 15a. 
Unlike the structure shown in FIG. 7, the one shown in FIG. 8 is designed to attach an insert without using a recess-projection fit or a pin fit and yet without using a wedging member. This design therefore can prevent the shift of the insert due to the centrifugal force caused by high-speed rotation and the distortion and strain of the tool body due to the tightening of the wedging member. However, the insert 12 is simply attached to the cartridge 13 with the insert-attaching screw 14. Consequently, the clamping force is weaker than that of a structure in which a wedging member is used. As a result, the insert-attaching screw 14 may fracture during high-speed rotation that applies considerable centrifugal force to the insert-attaching mechanism. Therefore, the structure shown in FIG. 8 alone cannot prevent the scattering of the inserts 12, though it can prevent the spring-out of the cartridges 13.
Under the above-described circumstances, the present invention offers a clamping mechanism that prevents the shift and scattering of inserts due to centrifugal force and that prevents the generation of unwanted distortion and strain in the rotary tool body.
The rotary cutting tool of the present invention has a plurality of inserts along the periphery of a cylindrical tool body. The inserts are securely attached to cartridges by using attaching screws The cartridges are then attached to the tool body. Each of the inserts is clamped such that a set screw screwed into the corresponding slanted threaded hole formed in the tool body presses the insert at its surface portion located on the other side of the attaching screw with respect to the cutting edge of the insert.